A Carnegie Institute of Washington team has developed a process that could lead to cheap, mass-produced, perfect diamonds of unlimited size, using chemical vapour deposition (CVD), where carbon atoms in a gas are deposited on a surface to produce diamond crystals.

They got around the size limit by using microwaves to “cook” their diamonds in a hydrogen plasma at 2200 degrees C but at low pressure. Diamond size is now limited only by the size of the microwave chamber used.